An annoying aspect of many conventional material handling trucks equipped with lifting forks is the tendency of the forks to rattle when the truck is travelling in an unloaded condition. It is desirable to minimize or eliminate this rattling to reduce the operational noise of the truck and also to create the impression that the truck is more solidly built.
Fork rattle generally arises from the mounting system used to mount the forks. One conventional way of mounting lift truck forks is to provide upper and lower carriage members or bars extending transversely across the mast of the lift truck and attaching the forks to these members. The upper carriage member has an upwardly extending ledge adjacent its outer face and the lower carriage member has a downwardly extending ledge adjacent its outer face. The fork is provided with upper and lower hangers having recesses for receiving the ledges of the carriage members to enable the forks to be slid over the ledges of the carriage members and laterally along the carriage members. As a pair of forks are generally used for material handling purposes, the slidability is desirable in order to enable the fork spacing to be altered to suit the various handling requirements.
In order to facilitate both the mounting of the fork and its slidability along the carriage member, the claw spacing and dimensions allow some clearance to minimize binding between the carriage members and the claws. This clearance however gives rise to rattling of the forks when there is no load on the forks to urge the forks or the retaining claws against the carriage members.
Various devices have been developed to take up the clearance between the hangers and the carriage members to stabilize the forks and thereby reduce their tendency to rattle. Examples of such devices are described in U.K. patent application 2l50ll2A, German patents 3318388 C2, 3340286 Cl and German Design Pat. No. G85l3646.8. These devices. The first type is a resilient strip which may be mechanically or adhesively securable to the carriage member or the hanger. The second type of device disclosed is a vertically movable plunger mounted to the shank of the lift truck fork and having a resilient plunger on its end that bears against the retaining ledge of the carriage bar. This latter type of device includes a biasing spring for urging the plunger toward the carriage bar.
A disadvantage with the first type of device is the amount of clearance which must be left between the hanger and the carriage member to accommodate the device. If the device were to be dislodged, as may easily happen during mounting or adjustment of the forks, an excessive clearance may be left between the hanger and the carriage member. With this excessive clearance, the fork may fail to meet some of the safety standards which set out maximum amounts of clearance for such structures. A further disadvantage to the first type of device is that it takes up the clearance between the hangers and the carriage members and thereby makes mounting and adjustment of the forks more difficult.
A disadvantage with the second type of device is its relative complexity which has an adverse effect on its manufacturing costs and the cost to install it on a fork. The second type of device also has the disadvantage that it does not have a retracted position and accordingly would interfere with mounting of the forks to the carriage members and subsequent adjustment of the forks.
It is apparent therefore that there is a need for a fork stabilizing device that is inexpensive, simple, easy to use and retractable so as not to interfere with mounting of the forks and their movement along the carriage members.